Scientists believe they may have discovered the secret to longevity for men -
but it comes at a painfully high price.

Researchers have shown that eunuchs living in Korea centuries ago outlived other men by a significant margin.

They say their findings suggest that male sex hormones are responsible for shortening the lives of men.

The evidence comes after study of genealogy records of noble members of the Imperial court of the Korean Chosun dynasty (AD 1392-1910).

Kyung-Jin Min, of Inha University, said: "This discovery adds an important clue for understanding why there is a difference in the expected life span between men and women."

The castrated boys in Korea lost their reproductive organs in accidents, usually after being bitten by dogs, or underwent castration purposefully to gain early access to the palace.

Eunuchs were allowed to marry and had families by adopting castrated boys or normal girls.

People in those days kept careful genealogy records as proof that they were of the noble class.

By poring over those records, Min and his colleague Cheol-Koo Lee, of Korea University, found that eunuchs lived 14 to 19 years longer than other men did.

Amongst the 81 eunuchs they studied, three lived to the age of 100 or more, a feat of longevity that remains relatively rare even in developed countries today.

They noted the incidence of centenarians among Korean eunuchs is at least 130 times greater than it is in the developed countries.

They argued the long life span cannot be explained simply by the benefits of life in the palace, as eunuchs spent as much time outside the palace as they did within it. Kings and male members of the royal family tend to have abnormally short lives, typically surviving only to their mid-forties.

The research team, whose findings were published in the journal Current Biology, said their findings may offer some clues to life extension.